1. Field of the Invention
The present invention relates to data transfer rate variance measurement method, apparatus, system, and storage medium for storing program used for evaluation of quality of a data communication or data transmitting apparatus, or the like.
2. Description of the Related Art
In general, a packet loss ratio or a delay time variance is used as an indicator representing a service quality of a packet data communication network. Particularly, the delay time variance has been considered as an important indicator in transfer of a real-time audio data or video data.
In the transfer of the real-time audio data or video data, data compression is generally performed. In many cases, although an initial rate for generation of real-time audio data or video data is constant, an output data rate at a compressor may be greatly varied as a result of the data compression process. In comparison with a traffic having a substantially constant data transfer rate, a traffic having a greatly-varying data transfer rate has an increasing packet loss and an increasing delay time variance although an average data transfer rate is equal.
Accordingly, in case of transferring the real-time audio data or video data, it is important to reduce the variance of the output data transfer rate at a transmitting apparatus for transmitting the real-time audio data or video data in addition to the improvement of service quality of the packet data communication network.
In addition, as a indicator of the service quality of the packet data communication network, a degree of an increase in the variance of the data transfer rate is important in a case where a packet transmitted from a data transmitting apparatus having a small variance of the output data transfer rate arrives at a receiving apparatus.
Therefore, it is important to perform measurement of output data transfer rate variance at the data transmission apparatus, for example, a server, and measurement of change in the data transfer rate variance in case of packets transmitted via a network.
In addition, in an apparatus used for measurement of quality of the network, the number of to-be-measured packets needs to be increased, but an amount of calculation for each one packet needs to be decreased. In addition, in the apparatus used for measurement of quality of the network, since various measurements may be independently and simultaneously performed according to classification of numbers representing packet transmitter ID, protocol, and the like and numbers representing receiver ID and the like, and the number of to-be-measured objects is increased, therefore a necessary amount of buffer (memory size) needs to be reduced.
Next, the definition of the data transfer rate in the present specification is described. In general, the data transfer rate represents an average transfer rate for a plurality of packets transferred within a predetermined time interval. However, in the specification, the data transfer rate is defined for each packet. Namely, it is assumed that a plurality of packets are transferred, a packet length of an i-th packet PKT(i) is denoted by L(i), a time point when the i-th packet PKT(i) is transferred is denoted by t(i), and a packet transfer time interval is denoted by Δt(i)=t(i)−t(i−1). In this case, the data transfer rate DTR(i) of the i-th packet is defined by the following Equation 1.DTR(i)=L(i)/(t(i)−t(i−1))=L(i)/Δt(i)  (Equation 1)
A generally-used data transfer rate is an average data transfer rate of packets PKT(1) to PKT(N) transferred within an arbitrary time interval, which is expressed by the following Equation 2.(Average Data Transfer Rate)=(ΣL(i))/(t(N)−t(0))=(ΣL(i))/(ΣΔt(i))  (Equation 2)
Here, Σ is a symbol representing a summation, and the summation in Equation 2 is performed from i=1 to i=N.
Next, it can be understood from Equation 1 that the variance of the data transfer rate has a close relationship with a variance of a time interval where two packets are transferred. In general, standard deviation or a value obtained by dividing the standard deviation by an average value is used as the indicator representing such a variance of a time interval.
Therefore, although a standard deviation of the data transfer rate expressed by Equation 1 or the value obtained by dividing the standard deviation by an average value may also be used as an indicator representing the data transfer rate variance, the standard deviation and the value obtained by dividing the standard deviation by the average value have not been used.
In addition, as a technology relating the present invention, in a case where a time interval between input packets and output packets and the number of accumulated packets have a normal logarithm probability density distribution, a value of acquisition probability of the number of packets up to a predetermined time point in a transmission queue of a transmission node is obtained by executing a standard normal probability density function 1−Φ(d), determining whether or not the value exceeds a predetermined reference value, evaluating a congestion state if the value is determined to exceed the predetermined reference value (refer to, for example Japanese Patent Application Laid-Open No. 2006-166425).
In addition, as a technology relating the present invention, quality evaluation is performed by calculating a mutual correlation function based on a packet passing time point sequence obtained by probing packets in each measurement apparatus, determining a generation period of a packet or a packet group, extracting a time point sequence within one period, and using a maximum value of correlation values in the time point sequence (refer to, for example, Japanese Patent No. 3834258).
Next, problems of the above-mentioned conventional technologies will be described as follows.
At first, the aforementioned Japanese Patent Application Laid-Open No. 2006-166425 and Japanese Patent No. 3834258 or related technologies have problems in that the data transfer rate variance indicator has not practically been used as a traffic quality indicator or a network service quality indicator.
This is because a data transfer rate variance indicator having a small amount of calculation for each one packet and a small necessary amount of buffer (memory size) and representing a suitable value has not been used.
The method of measuring an average and a standard deviation of a packet transfer time interval Δt(i) has problems as follows. In order to measure the average and the standard deviation of the Δt(i), the ΣΔt(i) and the Σ{Δt(i)**2} (hereinafter, (x**n) denotes an n-power of x) may be measured. Therefore, the indicator satisfies the conditions of a small amount of calculation for each one packet and a small necessary amount of buffer (memory size). However, in a case where the packet length L(i) is not constant, the data transfer rate cannot be estimated from the average and the standard deviation of the Δt(i).
Next, the method of measuring an average and a standard deviation of a data transfer rate DTR(i) has problems as follows. In the method of measuring the average and the standard deviation of the data transfer rate DTR(i), there is a problem of non-uniform distribution of the number of the measured samples. Since the measurement times of the DTR(i) is inversely proportional to the packet transfer time interval Δt(i), the number of data having a large value of DTR(i) is increased, but the number of data having a small value of DTR(i) is decreased.
Influence of the non-uniform distribution of the number of measured samples can be seen by analyzing the averages and the standard deviations of DTR(i) in the following three types of traffics.
Normal traffic: A packet having a packet length of 1100 bytes is transmitted every 2 ms.
ON_OFF traffic: Two transmission modes, that is, ON and OFF modes are alternately performed every 100 ms. In the ON mode, a packet having a packet length of 1000 bytes is transmitted every 2 ms, and in the OFF mode, any packet is not transmitted.
ON_OFF′ traffic: Two transmission modes, that is, ON and OFF′ modes are alternately performed every 100 ms. In the ON mode, a packet having a packet length of 900 bytes is transmitted every 2 ms, and in the OFF′ mode, a packet having a packet length of 50 bytes is transmitted every 2 ms.
The DTR(i) of the three types of traffics are illustrated in FIG. 1. The horizontal axis denotes a time ms, and the vertical axis denotes Mbps. Values of the average, the standard deviation, and the standard deviation/average of the DTR(i) of the three types of traffics are as follows.
In the normal traffic, the average is 4.40 Mbps, the standard deviation is 0.00 Mbps, and the standard deviation/average is 0.00.
In the.ON_OFF traffic, the average is 3.93 Mbps, the standard deviation is 0.52 Mbps, and the standard deviation/average is 0.13.
In the.ON_OFF′ traffic, the average is 1.93 Mbps, the standard deviation is 1.70 Mbps, and the standard deviation/average is 0.88.
It is preferable that, as the value of the indicator of traffic quality evaluation, the value of the ON_OFF traffic and the value of the ON_OFF′ traffic are selected to be substantially equal to each other, and the values of the two traffics are selected to be greatly different from the value of the normal traffic.
However, due to the non-uniform distribution of the measured data in the ON_OFF traffic, the value of the standard deviation/average in the ON_OFF traffic approaches the value of the normal traffic but it is greatly different from the value of the standard deviation/average in the ON_OFF′ traffic. Therefore, it can be understood that the standard deviation/average is not suitable for the indicator of the traffic quality evaluation.
In order to solve the above-mentioned problems, the present invention provides a data transfer rate variance measurement method, apparatus, system, and a storage medium for storing a program using a data transfer rate variance indicator having a small amount of calculation for each one packet, a small necessary amount of buffer (memory size), and representing a value suitable for traffic quality evaluation.